In the preparation of ceramic oxide materials of the kind referred to by mixing and co-milling of a metal and a ceramic oxide material and subsequent reaction-sintering, it has always keen desirable to use the metal in a particulate form with the smallest possible particle size Therefore, in many cases it has been attempted to use milled aluminum having a flake shape. A disadvantage of these processes has been, however, that the flakes smear and adhere to the millingbodies due to the softness of the metal and, hence, also mostly remain in a flake shape. See e.g., Nils Claussen et al. "Low-shrinkage Reaction-Bonded Alumina", J. Europ. Caram. Soc., 5, 1989, pages 29-35. See also other articles of and with Nils Claussen and his research group, such as "Tailoring of Reaction-Bonded Al.sub.2 O.sub.3 Ceramics" Corem Eng Sci Proc, 11, pages 806-820, 1990.
Another way to achieve a better homogeneity between metal and oxide materials in the present connection has been suggested for example, by the US firm Lanxide Corp., Newark, Del., USA and implies that an oxidation of the metal is carried out in melted form. See "Formation of Lanxide ceramic composite materials", J. Mater Res, 1, 1986, pages 81-89. Furthermore, Swedish patent No. 8103269-0 discloses a method of preparing shapes of silicon nitride based materials.